628 research outputs found
Statistical isotropy of the Cosmic Microwave Background
The breakdown of statistical homogeneity and isotropy of cosmic perturbations
is a generic feature of ultra large scale structure of the cosmos, in
particular, of non trivial cosmic topology. The statistical isotropy (SI) of
the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is
sensitive to this breakdown on the largest scales comparable to, and even
beyond the cosmic horizon. We propose a set of measures,
() which for non-zero values indicate and quantify statistical
isotropy violations in a CMB map. We numerically compute the predicted
spectra for CMB anisotropy in flat torus universe models.
Characteristic signature of different models in the spectrum are
noted.Comment: Presented at PASCOS'03, January 3-8, 2003, in TIFR, Mumbai; to be
published in a special issue of 'Pramana' (4 pages, 1 figure, style files
included
Interaction of Anticancer Drug Methotrexate with DS-DNA Analyzed by Spectroscopic and Electrochemical Methods
Abstract: Cyclic voltammetry coupled with UV/Vis spectroscopic techniques were used to study the interaction of methotrexate (MTX), an antitumor drug, with double stranded fish sperm DNA (ds-DNA) in phosphate buffer solution (pH 7.4). The interaction of MTX with DNA could result a considerable decrease in the MTX peak current. The variations in the spectroscopy and electrochemical characteristics of MTX indicated MTX bind to DNA by a groove binding mode. This conclusion was reinforced by viscosity data. The apparent transfer coefficients (α) and the number of electron transferred (n) of methotrexate in the absence and preset of ds-DNA have determined using anodic Tafel plots of MTX and MTX-DNA adduct on the surface of glassy carbone electrode. The diffusion coefficients of MTX in the absence (D 0 ) f and presence (D 0 ) b of DNA were calculated as 7.30×10 -6 and 3.40×10 -6 Cm 2 s -1 respectively. In spectrophotometric studies, the slopes of the calibration curves for methotrexate in the absence and presence of ds-DNA differ significantly. These studies are valuable for a better understanding the detailed mode of MTX-DNA interaction, which should be important in deeper insight into the therapeutic efficacy of MTX and design of new DNA targeted drug
Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. II. Orbits of Double-lined Spectroscopic Binaries
We present orbital parameters for six double-lined spectroscopic binaries
(iota Pegasi, omega Draconis, 12 Bootis, V1143 Cygni, beta Aurigae, and Mizar
A) and two double-lined triple star systems (kappa Pegasi and eta Virginis).
The orbital fits are based upon high-precision radial velocity observations
made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument
which combines interferometric and dispersive elements. For some of the
double-lined binaries with known inclination angles, the quality of our RV data
permits us to determine the masses M_1 and M_2 of the stellar components with
relative errors as small as 0.2%.Comment: 41 pages, 8 figures, accepted by A
Observational Study of the Multistructured Planetary Nebula NGC 7354
We present an observational study of the planetary nebula (PN) NGC 7354
consisting of narrowband Halpha and [NII]6584 imaging as well as low- and
high-dispersion long-slit spectroscopy and VLA-D radio continuum. According to
our imaging and spectroscopic data, NGC 7354 has four main structures: a quite
round outer shell and an elliptical inner shell, a collection of low-excitation
bright knots roughly concentrated on the equatorial region of the nebula, and
two symmetrical jet-like features, not aligned either with the shells' axes, or
with each other. We have obtained physical parameters like electron temperature
and electron density as well as ionic and elemental abundances for these
different structures. Electron temperature and electron density slightly vary
throughout the nebula. The local extinction coefficient c_Hbeta shows an
increasing gradient from south to north and a decreasing gradient from east to
west consistent with the number of equatorial bright knots present in each
direction. Abundance values show slight internal variations but most of them
are within the estimated uncertainties. In general, abundance values are in
good agreement with the ones expected for PNe. Radio continuum data are
consistent with optically thin thermal emission. We have used the interactive
three-dimensional modeling tool SHAPE to reproduce the observed morphokinematic
structures in NGC 7354 with different geometrical components. Our SHAPE model
is in very good agreement with our imaging and spectroscopic observations.
Finally, after modeling NGC 7354 with SHAPE, we suggest a possible scenario for
the formation of the nebula.Comment: Accepted for publication in AJ, 12 pages, 8 figure
Cosmological Imprints of Pre-Inflationary Particles
We study some of the cosmological imprints of pre-inflationary particles. We
show that each such particle provides a seed for a spherically symmetric cosmic
defect. The profile of this cosmic defect is fixed and its magnitude is linear
in a single parameter that is determined by the mass of the pre-inflationary
particle. We study the CMB and peculiar velocity imprints of this cosmic defect
and suggest that it could explain some of the large scale cosmological
anomalies.Comment: 31 pages, 7 figure
`Standard' Cosmological model & beyond with CMB
Observational Cosmology has indeed made very rapid progress in the past
decade. The ability to quantify the universe has largely improved due to
observational constraints coming from structure formation Measurements of CMB
anisotropy and, more recently, polarization have played a very important role.
Besides precise determination of various parameters of the `standard'
cosmological model, observations have also established some important basic
tenets that underlie models of cosmology and structure formation in the
universe -- `acausally' correlated initial perturbations in a flat,
statistically isotropic universe, adiabatic nature of primordial density
perturbations. These are consistent with the expectation of the paradigm of
inflation and the generic prediction of the simplest realization of
inflationary scenario in the early universe. Further, gravitational instability
is the established mechanism for structure formation from these initial
perturbations. The signature of primordial perturbations observed as the CMB
anisotropy and polarization is the most compelling evidence for new, possibly
fundamental, physics in the early universe. The community is now looking beyond
the estimation of parameters of a working `standard' model of cosmology for
subtle, characteristic signatures from early universe physics.Comment: 16 pages, 6 figures, Plenary talk, Proc. of GR-19, Mexico City,
Mexico (Jul 5-9, 2010). To appear in a special issue in Class. Q. Gra
Correlations in the (Sub)Mil1imeter Background from ACT x BLAST
We present measurements of the auto- and cross-frequency correlation power spectra of the cosmic (sub)millimeter background at: 250, 350, and 500 microns (1200, 860, and 600 GHz) from observations made with the Balloon-borne Large Aperture Submillimeter Telescope, BLAST; and at 1380 and 2030 microns (218 and 148 GHz) from observations made with the Atacama Cosmology Telescope, ACT. The overlapping observations cover 8.6 deg(sup 2) in an area relatively free of Galactic dust near the south ecliptic pole (SEP). The ACT bands are sensitive to radiation from the CMB, the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by radio and dusty star-forming galaxies (DSFGs), while the dominant contribution to the BLAST bands is from DSFGs. We confirm and extend the BLAST analysis of clustering with an independent pipeline, and also detect correlations between the ACT and BLAST maps at over 25(sigma) significance, which we interpret as a detection of the DSFGs in the ACT maps. In addition to a Poisson component in the cross-frequency power spectra, we detect a clustered signal at 4(sigma), and using a model for the DSFG evolution and number counts, we successfully fit all our spectra with a linear clustering model and a bias that depends only on red shift and not on scale. Finally, the data are compared to, and generally agree with, phenomenological models for the DSFG population. This study represents a first of its kind, and demonstrates the constraining power of the cross-frequency correlation technique to constrain models for the DSFGs. Similar analyses with more data will impose tight constraints 011 future models
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